Django documentation

Model field reference

This document contains all the gory details about all the field options and field types Django’s got to offer.

See also

If the built-in fields don’t do the trick, you can try django.contrib.localflavor, which contains assorted pieces of code that are useful for particular countries or cultures. Also, you can easily write your own custom model fields.

Note

Technically, these models are defined in django.db.models.fields, but for convenience they’re imported into django.db.models; the standard convention is to use from django.db import models and refer to fields as models.<Foo>Field.

Field options

The following arguments are available to all field types. All are optional.

null

Field.null

If True, Django will store empty values as NULL in the database. Default is False.

Note that empty string values will always get stored as empty strings, not as NULL. Only use null=True for non-string fields such as integers, booleans and dates. For both types of fields, you will also need to set blank=True if you wish to permit empty values in forms, as the null parameter only affects database storage (see blank).

Avoid using null on string-based fields such as CharField and TextField unless you have an excellent reason. If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string. In most cases, it’s redundant to have two possible values for “no data;” Django convention is to use the empty string, not NULL.

Note

When using the Oracle database backend, the value NULL will be stored to denote the empty string regardless of this attribute.

If you want to accept null values with BooleanField, use NullBooleanField instead.

blank

Field.blank

If True, the field is allowed to be blank. Default is False.

Note that this is different than null. null is purely database-related, whereas blank is validation-related. If a field has blank=True, form validation will allow entry of an empty value. If a field has blank=False, the field will be required.

choices

Field.choices

An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field. If this is given, the default form widget will be a select box with these choices instead of the standard text field.

The first element in each tuple is the actual value to be stored, and the second element is the human-readable name. For example:

YEAR_IN_SCHOOL_CHOICES = (
    ('FR', 'Freshman'),
    ('SO', 'Sophomore'),
    ('JR', 'Junior'),
    ('SR', 'Senior'),
)

Generally, it’s best to define choices inside a model class, and to define a suitably-named constant for each value:

class Student(models.Model):
    FRESHMAN = 'FR'
    SOPHOMORE = 'SO'
    JUNIOR = 'JR'
    SENIOR = 'SR'
    YEAR_IN_SCHOOL_CHOICES = (
        (FRESHMAN, 'Freshman'),
        (SOPHOMORE, 'Sophomore'),
        (JUNIOR, 'Junior'),
        (SENIOR, 'Senior'),
    )
    year_in_school = models.CharField(max_length=2,
                                      choices=YEAR_IN_SCHOOL_CHOICES,
                                      default=FRESHMAN)

    def is_upperclass(self):
        return self.year_in_school in (self.JUNIOR, self.SENIOR)

Though you can define a choices list outside of a model class and then refer to it, defining the choices and names for each choice inside the model class keeps all of that information with the class that uses it, and makes the choices easy to reference (e.g, Student.SOPHOMORE will work anywhere that the Student model has been imported).

You can also collect your available choices into named groups that can be used for organizational purposes:

MEDIA_CHOICES = (
    ('Audio', (
            ('vinyl', 'Vinyl'),
            ('cd', 'CD'),
        )
    ),
    ('Video', (
            ('vhs', 'VHS Tape'),
            ('dvd', 'DVD'),
        )
    ),
    ('unknown', 'Unknown'),
)

The first element in each tuple is the name to apply to the group. The second element is an iterable of 2-tuples, with each 2-tuple containing a value and a human-readable name for an option. Grouped options may be combined with ungrouped options within a single list (such as the unknown option in this example).

For each model field that has choices set, Django will add a method to retrieve the human-readable name for the field’s current value. See get_FOO_display() in the database API documentation.

Finally, note that choices can be any iterable object – not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you’re probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn’t change much, if ever.

db_column

Field.db_column

The name of the database column to use for this field. If this isn’t given, Django will use the field’s name.

If your database column name is an SQL reserved word, or contains characters that aren’t allowed in Python variable names – notably, the hyphen – that’s OK. Django quotes column and table names behind the scenes.

db_index

Field.db_index

If True, django-admin.py sqlindexes will output a CREATE INDEX statement for this field.

db_tablespace

Field.db_tablespace

The name of the database tablespace to use for this field’s index, if this field is indexed. The default is the project’s DEFAULT_INDEX_TABLESPACE setting, if set, or the db_tablespace of the model, if any. If the backend doesn’t support tablespaces for indexes, this option is ignored.

default

Field.default

The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.

The default cannot be a mutable object (model instance, list, set, etc.), as a reference to the same instance of that object would be used as the default value in all new model instances. Instead, wrap the desired default in a callable. For example, if you had a custom JSONField and wanted to specify a dictionary as the default, use a lambda as follows:

contact_info = JSONField("ContactInfo", default=lambda:{"email": "to1@example.com"})

editable

Field.editable

If False, the field will not be displayed in the admin or any other ModelForm. Default is True.

error_messages

Field.error_messages

The error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override.

Error message keys include null, blank, invalid, invalid_choice, and unique. Additional error message keys are specified for each field in the Field types section below.

help_text

Field.help_text

Extra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.

Note that this value is not HTML-escaped in automatically-generated forms. This lets you include HTML in help_text if you so desire. For example:

help_text="Please use the following format: <em>YYYY-MM-DD</em>."

Alternatively you can use plain text and django.utils.html.escape() to escape any HTML special characters.

primary_key

Field.primary_key

If True, this field is the primary key for the model.

If you don’t specify primary_key=True for any field in your model, Django will automatically add an AutoField to hold the primary key, so you don’t need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior. For more, see Automatic primary key fields.

primary_key=True implies null=False and unique=True. Only one primary key is allowed on an object.

unique

Field.unique

If True, this field must be unique throughout the table.

This is enforced at the database level and by model validation. If you try to save a model with a duplicate value in a unique field, a django.db.IntegrityError will be raised by the model’s save() method.

This option is valid on all field types except ManyToManyField, OneToOneField, and FileField.

Note that when unique is True, you don’t need to specify db_index, because unique implies the creation of an index.

unique_for_date

Field.unique_for_date

Set this to the name of a DateField or DateTimeField to require that this field be unique for the value of the date field.

For example, if you have a field title that has unique_for_date="pub_date", then Django wouldn’t allow the entry of two records with the same title and pub_date.

This is enforced by model validation but not at the database level.

unique_for_month

Field.unique_for_month

Like unique_for_date, but requires the field to be unique with respect to the month.

unique_for_year

Field.unique_for_year

Like unique_for_date and unique_for_month.

verbose_name

Field.verbose_name

A human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces. See Verbose field names.

validators

Field.validators

A list of validators to run for this field. See the validators documentation for more information.

Field types

AutoField

class AutoField(**options)

An IntegerField that automatically increments according to available IDs. You usually won’t need to use this directly; a primary key field will automatically be added to your model if you don’t specify otherwise. See Automatic primary key fields.

BigIntegerField

class BigIntegerField([**options])

A 64 bit integer, much like an IntegerField except that it is guaranteed to fit numbers from -9223372036854775808 to 9223372036854775807. The default form widget for this field is a TextInput.

BooleanField

class BooleanField(**options)

A true/false field.

The default form widget for this field is a CheckboxInput.

If you need to accept null values then use NullBooleanField instead.

CharField

class CharField(max_length=None[, **options])

A string field, for small- to large-sized strings.

For large amounts of text, use TextField.

The default form widget for this field is a TextInput.

CharField has one extra required argument:

CharField.max_length

The maximum length (in characters) of the field. The max_length is enforced at the database level and in Django’s validation.

Note

If you are writing an application that must be portable to multiple database backends, you should be aware that there are restrictions on max_length for some backends. Refer to the database backend notes for details.

MySQL users

If you are using this field with MySQLdb 1.2.2 and the utf8_bin collation (which is not the default), there are some issues to be aware of. Refer to the MySQL database notes for details.

CommaSeparatedIntegerField

class CommaSeparatedIntegerField(max_length=None[, **options])

A field of integers separated by commas. As in CharField, the max_length argument is required and the note about database portability mentioned there should be heeded.

DateField

class DateField([auto_now=False, auto_now_add=False, **options])

A date, represented in Python by a datetime.date instance. Has a few extra, optional arguments:

DateField.auto_now

Automatically set the field to now every time the object is saved. Useful for “last-modified” timestamps. Note that the current date is always used; it’s not just a default value that you can override.

DateField.auto_now_add

Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it’s not just a default value that you can override.

The default form widget for this field is a TextInput. The admin adds a JavaScript calendar, and a shortcut for “Today”. Includes an additional invalid_date error message key.

Note

As currently implemented, setting auto_now or auto_now_add to True will cause the field to have editable=False and blank=True set.

DateTimeField

class DateTimeField([auto_now=False, auto_now_add=False, **options])

A date and time, represented in Python by a datetime.datetime instance. Takes the same extra arguments as DateField.

The default form widget for this field is a single TextInput. The admin uses two separate TextInput widgets with JavaScript shortcuts.

DecimalField

class DecimalField(max_digits=None, decimal_places=None[, **options])

A fixed-precision decimal number, represented in Python by a Decimal instance. Has two required arguments:

DecimalField.max_digits

The maximum number of digits allowed in the number. Note that this number must be greater than or equal to decimal_places.

DecimalField.decimal_places

The number of decimal places to store with the number.

For example, to store numbers up to 999 with a resolution of 2 decimal places, you’d use:

models.DecimalField(..., max_digits=5, decimal_places=2)

And to store numbers up to approximately one billion with a resolution of 10 decimal places:

models.DecimalField(..., max_digits=19, decimal_places=10)

The default form widget for this field is a TextInput.

Note

For more information about the differences between the FloatField and DecimalField classes, please see FloatField vs. DecimalField.

EmailField

class EmailField([max_length=75, **options])

A CharField that checks that the value is a valid email address.

Incompliance to RFCs

The default 75 character max_length is not capable of storing all possible RFC3696/5321-compliant email addresses. In order to store all possible valid email addresses, a max_length of 254 is required. The default max_length of 75 exists for historical reasons. The default has not been changed in order to maintain backwards compatibility with existing uses of EmailField.

FileField

class FileField(upload_to=None[, max_length=100, **options])

A file-upload field.

Note

The primary_key and unique arguments are not supported, and will raise a TypeError if used.

Has one required argument:

FileField.upload_to

A local filesystem path that will be appended to your MEDIA_ROOT setting to determine the value of the url attribute.

This path may contain strftime() formatting, which will be replaced by the date/time of the file upload (so that uploaded files don’t fill up the given directory).

This may also be a callable, such as a function, which will be called to obtain the upload path, including the filename. This callable must be able to accept two arguments, and return a Unix-style path (with forward slashes) to be passed along to the storage system. The two arguments that will be passed are:

Argument Description
instance

An instance of the model where the FileField is defined. More specifically, this is the particular instance where the current file is being attached.

In most cases, this object will not have been saved to the database yet, so if it uses the default AutoField, it might not yet have a value for its primary key field.

filename The filename that was originally given to the file. This may or may not be taken into account when determining the final destination path.

Also has one optional argument:

FileField.storage

Optional. A storage object, which handles the storage and retrieval of your files. See Managing files for details on how to provide this object.

The default form widget for this field is a ClearableFileInput.

Using a FileField or an ImageField (see below) in a model takes a few steps:

  1. In your settings file, you’ll need to define MEDIA_ROOT as the full path to a directory where you’d like Django to store uploaded files. (For performance, these files are not stored in the database.) Define MEDIA_URL as the base public URL of that directory. Make sure that this directory is writable by the Web server’s user account.
  2. Add the FileField or ImageField to your model, making sure to define the upload_to option to tell Django to which subdirectory of MEDIA_ROOT it should upload files.
  3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You’ll most likely want to use the convenience url attribute provided by Django. For example, if your ImageField is called mug_shot, you can get the absolute path to your image in a template with {{ object.mug_shot.url }}.

For example, say your MEDIA_ROOT is set to '/home/media', and upload_to is set to 'photos/%Y/%m/%d'. The '%Y/%m/%d' part of upload_to is strftime() formatting; '%Y' is the four-digit year, '%m' is the two-digit month and '%d' is the two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in the directory /home/media/photos/2007/01/15.

If you wanted to retrieve the uploaded file’s on-disk filename, or the file’s size, you could use the name and size attributes respectively; for more information on the available attributes and methods, see the File class reference and the Managing files topic guide.

Note

The file is saved as part of saving the model in the database, so the actual file name used on disk cannot be relied on until after the model has been saved.

The uploaded file’s relative URL can be obtained using the url attribute. Internally, this calls the url() method of the underlying Storage class.

Note that whenever you deal with uploaded files, you should pay close attention to where you’re uploading them and what type of files they are, to avoid security holes. Validate all uploaded files so that you’re sure the files are what you think they are. For example, if you blindly let somebody upload files, without validation, to a directory that’s within your Web server’s document root, then somebody could upload a CGI or PHP script and execute that script by visiting its URL on your site. Don’t allow that.

Also note that even an uploaded HTML file, since it can be executed by the browser (though not by the server), can pose security threats that are equivalent to XSS or CSRF attacks.

By default, FileField instances are created as varchar(100) columns in your database. As with other fields, you can change the maximum length using the max_length argument.

FileField and FieldFile

class FieldFile

When you access a FileField on a model, you are given an instance of FieldFile as a proxy for accessing the underlying file. This class has several attributes and methods that can be used to interact with file data:

FieldFile.url

A read-only property to access the file’s relative URL by calling the url() method of the underlying Storage class.

FieldFile.open(mode='rb')

Behaves like the standard Python open() method and opens the file associated with this instance in the mode specified by mode.

FieldFile.close()

Behaves like the standard Python file.close() method and closes the file associated with this instance.

FieldFile.save(name, content, save=True)

This method takes a filename and file contents and passes them to the storage class for the field, then associates the stored file with the model field. If you want to manually associate file data with FileField instances on your model, the save() method is used to persist that file data.

Takes two required arguments: name which is the name of the file, and content which is an object containing the file’s contents. The optional save argument controls whether or not the instance is saved after the file has been altered. Defaults to True.

Note that the content argument should be an instance of django.core.files.File, not Python’s built-in file object. You can construct a File from an existing Python file object like this:

from django.core.files import File
# Open an existing file using Python's built-in open()
f = open('/tmp/hello.world')
myfile = File(f)

Or you can construct one from a Python string like this:

from django.core.files.base import ContentFile
myfile = ContentFile("hello world")

For more information, see Managing files.

FieldFile.delete(save=True)

Deletes the file associated with this instance and clears all attributes on the field. Note: This method will close the file if it happens to be open when delete() is called.

The optional save argument controls whether or not the instance is saved after the file has been deleted. Defaults to True.

Note that when a model is deleted, related files are not deleted. If you need to cleanup orphaned files, you’ll need to handle it yourself (for instance, with a custom management command that can be run manually or scheduled to run periodically via e.g. cron).

FilePathField

class FilePathField(path=None[, match=None, recursive=False, max_length=100, **options])

A CharField whose choices are limited to the filenames in a certain directory on the filesystem. Has three special arguments, of which the first is required:

FilePathField.path

Required. The absolute filesystem path to a directory from which this FilePathField should get its choices. Example: "/home/images".

FilePathField.match

Optional. A regular expression, as a string, that FilePathField will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example: "foo.*\.txt$", which will match a file called foo23.txt but not bar.txt or foo23.png.

FilePathField.recursive

Optional. Either True or False. Default is False. Specifies whether all subdirectories of path should be included

FilePathField.allow_files
New in Django 1.5.

Optional. Either True or False. Default is True. Specifies whether files in the specified location should be included. Either this or allow_folders must be True.

FilePathField.allow_folders
New in Django 1.5.

Optional. Either True or False. Default is False. Specifies whether folders in the specified location should be included. Either this or allow_files must be True.

Of course, these arguments can be used together.

The one potential gotcha is that match applies to the base filename, not the full path. So, this example:

FilePathField(path="/home/images", match="foo.*", recursive=True)

...will match /home/images/foo.png but not /home/images/foo/bar.png because the match applies to the base filename (foo.png and bar.png).

By default, FilePathField instances are created as varchar(100) columns in your database. As with other fields, you can change the maximum length using the max_length argument.

FloatField

class FloatField([**options])

A floating-point number represented in Python by a float instance.

The default form widget for this field is a TextInput.

FloatField vs. DecimalField

The FloatField class is sometimes mixed up with the DecimalField class. Although they both represent real numbers, they represent those numbers differently. FloatField uses Python’s float type internally, while DecimalField uses Python’s Decimal type. For information on the difference between the two, see Python’s documentation for the decimal module.

ImageField

class ImageField(upload_to=None[, height_field=None, width_field=None, max_length=100, **options])

Inherits all attributes and methods from FileField, but also validates that the uploaded object is a valid image.

In addition to the special attributes that are available for FileField, an ImageField also has height and width attributes.

To facilitate querying on those attributes, ImageField has two extra optional arguments:

ImageField.height_field

Name of a model field which will be auto-populated with the height of the image each time the model instance is saved.

ImageField.width_field

Name of a model field which will be auto-populated with the width of the image each time the model instance is saved.

Requires the Python Imaging Library.

By default, ImageField instances are created as varchar(100) columns in your database. As with other fields, you can change the maximum length using the max_length argument.

The default form widget for this field is a ClearableFileInput.

IntegerField

class IntegerField([**options])

An integer. The default form widget for this field is a TextInput.

IPAddressField

class IPAddressField([**options])

An IP address, in string format (e.g. “192.0.2.30”). The default form widget for this field is a TextInput.

GenericIPAddressField

class GenericIPAddressField([protocol=both, unpack_ipv4=False, **options])
New in Django 1.4.

An IPv4 or IPv6 address, in string format (e.g. 192.0.2.30 or 2a02:42fe::4). The default form widget for this field is a TextInput.

The IPv6 address normalization follows RFC 4291 section 2.2, including using the IPv4 format suggested in paragraph 3 of that section, like ::ffff:192.0.2.0. For example, 2001:0::0:01 would be normalized to 2001::1, and ::ffff:0a0a:0a0a to ::ffff:10.10.10.10. All characters are converted to lowercase.

GenericIPAddressField.protocol

Limits valid inputs to the specified protocol. Accepted values are 'both' (default), 'IPv4' or 'IPv6'. Matching is case insensitive.

GenericIPAddressField.unpack_ipv4

Unpacks IPv4 mapped addresses like ::ffff:192.0.2.1. If this option is enabled that address would be unpacked to 192.0.2.1. Default is disabled. Can only be used when protocol is set to 'both'.

NullBooleanField

class NullBooleanField([**options])

Like a BooleanField, but allows NULL as one of the options. Use this instead of a BooleanField with null=True. The default form widget for this field is a NullBooleanSelect.

PositiveIntegerField

class PositiveIntegerField([**options])

Like an IntegerField, but must be either positive or zero (0). The value 0 is accepted for backward compatibility reasons.

PositiveSmallIntegerField

class PositiveSmallIntegerField([**options])

Like a PositiveIntegerField, but only allows values under a certain (database-dependent) point. Values up to 32767 are safe in all databases supported by Django.

SlugField

class SlugField([max_length=50, **options])

Slug is a newspaper term. A slug is a short label for something, containing only letters, numbers, underscores or hyphens. They’re generally used in URLs.

Like a CharField, you can specify max_length (read the note about database portability and max_length in that section, too). If max_length is not specified, Django will use a default length of 50.

Implies setting Field.db_index to True.

It is often useful to automatically prepopulate a SlugField based on the value of some other value. You can do this automatically in the admin using prepopulated_fields.

SmallIntegerField

class SmallIntegerField([**options])

Like an IntegerField, but only allows values under a certain (database-dependent) point. Values from -32768 to 32767 are safe in all databases supported by Django.

TextField

class TextField([**options])

A large text field. The default form widget for this field is a Textarea.

MySQL users

If you are using this field with MySQLdb 1.2.1p2 and the utf8_bin collation (which is not the default), there are some issues to be aware of. Refer to the MySQL database notes for details.

TimeField

class TimeField([auto_now=False, auto_now_add=False, **options])

A time, represented in Python by a datetime.time instance. Accepts the same auto-population options as DateField.

The default form widget for this field is a TextInput. The admin adds some JavaScript shortcuts.

URLField

class URLField([max_length=200, **options])

A CharField for a URL.

The default form widget for this field is a TextInput.

Like all CharField subclasses, URLField takes the optional max_length argument. If you don’t specify max_length, a default of 200 is used.

New in Django 1.5.

The current value of the field will be displayed as a clickable link above the input widget.

Relationship fields

Django also defines a set of fields that represent relations.

ForeignKey

class ForeignKey(othermodel[, **options])

A many-to-one relationship. Requires a positional argument: the class to which the model is related.

To create a recursive relationship – an object that has a many-to-one relationship with itself – use models.ForeignKey('self').

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

class Car(models.Model):
    manufacturer = models.ForeignKey('Manufacturer')
    # ...

class Manufacturer(models.Model):
    # ...

To refer to models defined in another application, you can explicitly specify a model with the full application label. For example, if the Manufacturer model above is defined in another application called production, you’d need to use:

class Car(models.Model):
    manufacturer = models.ForeignKey('production.Manufacturer')

This sort of reference can be useful when resolving circular import dependencies between two applications.

A database index is automatically created on the ForeignKey. You can disable this by setting db_index to False. You may want to avoid the overhead of an index if you are creating a foreign key for consistency rather than joins, or if you will be creating an alternative index like a partial or multiple column index.

Database Representation

Behind the scenes, Django appends "_id" to the field name to create its database column name. In the above example, the database table for the Car model will have a manufacturer_id column. (You can change this explicitly by specifying db_column) However, your code should never have to deal with the database column name, unless you write custom SQL. You’ll always deal with the field names of your model object.

Arguments

ForeignKey accepts an extra set of arguments – all optional – that define the details of how the relation works.

ForeignKey.limit_choices_to

A dictionary of lookup arguments and values (see Making queries) that limit the available admin or ModelForm choices for this object. For example:

staff_member = models.ForeignKey(User, limit_choices_to={'is_staff': True})

causes the corresponding field on the ModelForm to list only Users that have is_staff=True.

Instead of a dictionary this can also be a Q object for more complex queries. However, if limit_choices_to is a Q object then it will only have an effect on the choices available in the admin when the field is not listed in raw_id_fields in the ModelAdmin for the model.

ForeignKey.related_name

The name to use for the relation from the related object back to this one. See the related objects documentation for a full explanation and example. Note that you must set this value when defining relations on abstract models; and when you do so some special syntax is available.

If you’d prefer Django not to create a backwards relation, set related_name to '+' or end it with '+'. For example, this will ensure that the User model won’t have a backwards relation to this model:

user = models.ForeignKey(User, related_name='+')
ForeignKey.to_field

The field on the related object that the relation is to. By default, Django uses the primary key of the related object.

ForeignKey.on_delete

When an object referenced by a ForeignKey is deleted, Django by default emulates the behavior of the SQL constraint ON DELETE CASCADE and also deletes the object containing the ForeignKey. This behavior can be overridden by specifying the on_delete argument. For example, if you have a nullable ForeignKey and you want it to be set null when the referenced object is deleted:

user = models.ForeignKey(User, blank=True, null=True, on_delete=models.SET_NULL)

The possible values for on_delete are found in django.db.models:

  • CASCADE

    Cascade deletes; the default.

  • PROTECT

    Prevent deletion of the referenced object by raising ProtectedError, a subclass of django.db.IntegrityError.

  • SET_NULL

    Set the ForeignKey null; this is only possible if null is True.

  • SET_DEFAULT

    Set the ForeignKey to its default value; a default for the ForeignKey must be set.

  • SET()

    Set the ForeignKey to the value passed to SET(), or if a callable is passed in, the result of calling it. In most cases, passing a callable will be necessary to avoid executing queries at the time your models.py is imported:

    def get_sentinel_user():
        return User.objects.get_or_create(username='deleted')[0]
    
    class MyModel(models.Model):
        user = models.ForeignKey(User, on_delete=models.SET(get_sentinel_user))
    
  • DO_NOTHING

    Take no action. If your database backend enforces referential integrity, this will cause an IntegrityError unless you manually add a SQL ON DELETE constraint to the database field (perhaps using initial sql).

ManyToManyField

class ManyToManyField(othermodel[, **options])

A many-to-many relationship. Requires a positional argument: the class to which the model is related, which works exactly the same as it does for ForeignKey, including recursive and lazy relationships.

Related objects can be added, removed, or created with the field’s RelatedManager.

Database Representation

Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship. By default, this table name is generated using the name of the many-to-many field and the name of the table for the model that contains it. Since some databases don’t support table names above a certain length, these table names will be automatically truncated to 64 characters and a uniqueness hash will be used. This means you might see table names like author_books_9cdf4; this is perfectly normal. You can manually provide the name of the join table using the db_table option.

Arguments

ManyToManyField accepts an extra set of arguments – all optional – that control how the relationship functions.

ManyToManyField.related_name

Same as ForeignKey.related_name.

If you have more than one ManyToManyField pointing to the same model and want to suppress the backwards relations, set each related_name to a unique value ending with '+':

users = models.ManyToManyField(User, related_name='u+')
referents = models.ManyToManyField(User, related_name='ref+')
ManyToManyField.limit_choices_to

Same as ForeignKey.limit_choices_to.

limit_choices_to has no effect when used on a ManyToManyField with a custom intermediate table specified using the through parameter.

ManyToManyField.symmetrical

Only used in the definition of ManyToManyFields on self. Consider the following model:

class Person(models.Model):
    friends = models.ManyToManyField("self")

When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn’t add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical – that is, if I am your friend, then you are my friend.

If you do not want symmetry in many-to-many relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToManyField relationships to be non-symmetrical.

ManyToManyField.through

Django will automatically generate a table to manage many-to-many relationships. However, if you want to manually specify the intermediary table, you can use the through option to specify the Django model that represents the intermediate table that you want to use.

The most common use for this option is when you want to associate extra data with a many-to-many relationship.

ManyToManyField.db_table

The name of the table to create for storing the many-to-many data. If this is not provided, Django will assume a default name based upon the names of: the table for the model defining the relationship and the name of the field itself.

OneToOneField

class OneToOneField(othermodel[, parent_link=False, **options])

A one-to-one relationship. Conceptually, this is similar to a ForeignKey with unique=True, but the “reverse” side of the relation will directly return a single object.

This is most useful as the primary key of a model which “extends” another model in some way; Multi-table inheritance is implemented by adding an implicit one-to-one relation from the child model to the parent model, for example.

One positional argument is required: the class to which the model will be related. This works exactly the same as it does for ForeignKey, including all the options regarding recursive and lazy relationships.

If you do not specify the the related_name argument for the OneToOneField, Django will use the lower-case name of the current model as default value.

With the following example:

from django.db import models
from django.contrib.auth.models import User

class MySpecialUser(models.Model):
    user = models.OneToOneField(User)
    supervisor = models.OneToOneField(User, related_name='supervisor_of')

your resulting User model will have the following attributes:

>>> user = User.objects.get(pk=1)
>>> hasattr(user, 'myspecialuser')
True
>>> hasattr(user, 'supervisor_of')
True

Additionally, OneToOneField accepts all of the extra arguments accepted by ForeignKey, plus one extra argument:

When True and used in a model which inherits from another (concrete) model, indicates that this field should be used as the link back to the parent class, rather than the extra OneToOneField which would normally be implicitly created by subclassing.

See One-to-one relationships for usage examples of OneToOneField.

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